Combustion engine exhaust after-treatment system incorporating syngas generator

ABSTRACT

A combustion engine exhaust after-treatment system includes a syngas generator for producing a syngas stream. The syngas stream is supplied to one or more parts of the engine system resulting in reduced emissions and/or reduced fuel consumption. The syngas generator produces a syngas stream via chemical reaction of the engine exhaust stream with a fuel stream.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation-in-part of U.S. patent application Ser. No. 11/193,930 entitled “Integrated System for Reducing Fuel Consumption and Emissions in an Internal Combustion Engine” filed on Jul. 29, 2005, which claims priority benefits from U.S. Provisional Patent Application No. 60/592,050 and filed on Jul. 29, 2004 and U.S. Provisional Patent Application No. 60/640,936 filed on Dec. 30, 2004. The '930, '050 and '936 applications are each hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to the after-treatment of combustion engine exhaust streams to reduce the amount of deleterious constituents in the exhaust streams. More particularly, the present invention relates to a combustion engine exhaust after-treatment system that incorporates a reducing agent generator for supplying a hydrogen-containing stream to one or more parts of the engine system resulting in reduced emissions and/or reduced fuel consumption.

BACKGROUND OF THE INVENTION

Over the past decades, government-imposed diesel engine emission regulations have been met by various component design modifications and engine control techniques. In general, these changes have resulted in increasing both the capital and operating costs.

The two primary techniques that have been deployed to reduce emissions are:

-   -   (1) retarding fuel injection timing to reduce engine exhaust NOx         levels; and     -   (2) employing exhaust gas recirculation (EGR) to lower the         in-cylinder combustion temperatures and thus reduce engine         exhaust NOx levels.         Each of these techniques also has the undesirable effect of         increasing fuel consumption.

Examples of other component design modifications and engine control techniques that have been used to reduce emissions include:

-   -   (a) redesign of engine cylinders to promote more effective         fuel/air mixing;     -   (b) improved fuel injector spray patterns to provide more         effective air/fuel mixing;     -   (c) more efficient turbo-compressor designs; and     -   (d) more precise control of fuel injection quantities based on         engine speed and torque.         Some of these examples have an additional desirable effect of         reducing fuel consumption. These and other approaches are         detailed in the open literature (see, for example,         www.dieselnet.com).

The diesel engine industry is now in general agreement that meeting upcoming diesel engine emission regulations will be virtually impossible using the conventional approaches of component design modifications and control techniques. Moreover, the industry generally agrees that the incorporation of exhaust after-treatment systems will be required to meet upcoming emission regulations. Thus, while the diesel engine industry continues to develop so-called “in-cylinder” solutions in efforts to comply with emission regulations, significant efforts are now being devoted to the development of exhaust “after-treatment” solutions, including the development of after-treatment equipment and operating techniques for remediating harmful exhaust emissions.

FIG. 1 shows a representative conventional (prior art) diesel engine system with an exhaust module that has been used in medium and heavy duty trucks and other such vehicles both on-road and off-road. The system components denoted in FIG. 1 and their operative connections will be described hereinafter in the Detailed Description of Preferred Embodiment(s) section.

Diesel engines have two different types of emissions that are of primary concern: (1) particulate matter (PM), which is the soot and carbon particles emitted from a diesel engine exhaust pipe in the form of a black cloud (PM has been linked to cancer and other diseases), and (2) nitrogen oxides (NOx), which are linked to respiratory problems, as well as being strong greenhouse gas pollutants.

To meet the upcoming government-imposed particulate matter (PM) emission regulations, the diesel engine industry is generally planning to employ filtering devices that trap the PM present in engine exhaust streams. These filters are periodically regenerated in-situ during operation, either passively or by using specific active control techniques, some of which employ diesel fuel to assist in oxidizing the carbon collected on the filter. Some other filter designs are designed to be cleaned during scheduled maintenance to ensure the continued trapping of PM and adherence to PM emission regulations. If the filtering device contains catalytic material it is referred to as a catalyzed diesel particulate filter (CDPF) and if not, it is simply referred to as a diesel particulate filter (DPF).

The removal of NOx generally takes place with the use of a catalyst bed. One technique being proposed as a method of reducing NOx emissions from diesel engines is called urea selective catalytic reduction (UREA-SCR). In this technique, aqueous urea is sprayed into a catalytic bed in an amount that essentially matches the amount of NOx to be reduced. The urea breaks down into ammonia components and then chemically reduces the NOx into nitrogen gas (N₂) and water. As with most technologies, UREA-SCR has advantages and disadvantages. Presently UREA-SCR has attracted significant interest in Europe. North American companies are also considering using UREA-SCR to remediate their engine exhaust streams, but appear to be favoring a system that utilizes a catalyst and adsorbent bed to trap the NOx, and then periodically regenerates these beds to restore their effectiveness to remove NOx from the engine exhaust stream.

Typically, the NOx trapping is performed by passing the entire engine exhaust stream through the catalyst and adsorbent bed. Oxygen present in the exhaust stream reacts over a platinum catalyst with NO in the exhaust stream, yielding NO₂ (see Equation (1) below). The NO₂ then adsorbs onto the bed adsorbent. A typical adsorbent material is barium oxide, in which case barium nitrate is formed in the adsorption reaction (see Equation (2) below). This type of catalytic/adsorbent bed is often referred to as a “lean NOx trap” (LNT), since NOx is trapped while the bed is in a lean (excess oxygen) environment. When the capacity of the LNT to adsorb NOx from the engine exhaust stream has been met, or prior to this point, the bed is regenerated. Under fuel rich and/or higher temperature conditions the nitrate species become thermodynamically unstable and decompose, producing NO or NO₂, according to Equations (3a) and (3b). These nitrogen oxides are subsequently reduced (e.g. by carbon monoxide, hydrogen and/or hydrocarbons) to nitrogen (N₂) over the reduction catalyst (Reaction (4) below). Small quantities of ammonia (NH₃) and N₂O may also be formed during the regeneration mode.

Thus, the following chemical reactions occur in a typical LNT: Oxidation: NO+½O₂→NO₂   (1) Adsorption: NO₂+BaO+½O₂→Ba(NO₃)₂   (2) Desorption of NO₃: Ba(NO₃)₂═BaO+2NO+ 3/2O₂   (3a) Ba(NO₃)₂═BaO+2NO₂+½O₂   (3b) Reduction of NOx to N₂, H₂O and CO₂   (4)

FIG. 2 is a schematic diagram illustrating the catalytic mechanisms involved in trapping and regeneration modes of typical LNTs. The diagram on the left of the page shows the trapping (lean) mechanism, which involves the initial oxidation of NO to NO₂ over a platinum catalyst (reaction (1) above) and subsequent adsorption of NO₂ onto barium oxide (BaO) catalyst sites to form an inorganic nitrate, Ba(NO₃)₂ (reaction (2) above). The diagram on the right of the page shows the regeneration (rich) mechanism, which involves the desorption of NOx from the BaO catalyst sites, in the presence of diesel fuel (reactions (3a) and (3b) above), and the subsequent reduction of NOx compounds primarily to N₂, H₂O and CO₂ (reaction (4) above).

Besides dealing with PM and NOx, the quantity of unburned hydrocarbons (HC) and carbon monoxide (CO) present in a diesel engine exhaust stream can be reduced by passing the exhaust stream through a catalytic bed. This is typically referred to as a diesel oxidation catalyst (DOC) technique. The HC and CO are oxidized with oxygen present in the exhaust stream over a platinum catalyst that is typically wash-coated onto a cordierite monolith. The DOC has similarities to the catalytic converter employed in connection with gasoline-fueled combustion engines for passenger cars.

FIG. 3 shows a representative conventional (prior art) diesel engine system that employs catalysts and adsorbents to remediate the engine exhaust stream. Although FIG. 3 shows a CDPF, LNT and DOC in specific positions within the exhaust system, equally effective systems can be devised with such exhaust after-treatment components arranged in a different sequence. The system components denoted in FIG. 3 and their operative connections will be described hereinafter in the Detailed Description of Preferred Embodiment(s) section.

In the approach described herein, a combustion engine system incorporates a reducing agent generator, such as a syngas generator, for supplying a hydrogen-containing stream to one or more parts of the engine system including the engine exhaust after-treatment system, resulting in reduced emissions and/or reduced fuel consumption.

SUMMARY OF THE INVENTION

In various embodiments, a method for operating an engine system comprising an exhaust after-treatment system and a syngas generator comprises directing a fuel stream from a fuel supply to the engine, and directing an air stream to the engine via an air intake line, and operating the engine to produce an engine exhaust stream. The syngas generator is operated to produce a syngas stream. Some or all of the engine exhaust stream is at least periodically directed to one or more exhaust after-treatment devices in the exhaust after-treatment system, for reducing regulated emissions from the engine system. Some or all of the syngas stream is at least periodically directed to one or more of the exhaust after-treatment devices for heating or regenerating the device. The syngas stream exiting such devices is referred to as a depleted syngas stream. This depleted syngas stream and/or additional syngas produced by the syngas generator is directed back to the engine via the air intake line.

In various embodiments a combustion engine and after-treatment system includes a fuel tank and fuel supply subsystem for directing fuel to the engine, and an air supply subsystem for directing an air stream to the engine via an air intake line. An engine exhaust stream line is connected to receive an exhaust stream from the engine. One or more exhaust after-treatment devices are connected to separately receive engine exhaust stream and/or syngas from a syngas generator. For example devices such as a DPF and DOC may be connected to receive syngas, and a LNT may be connected to receive both engine exhaust and syngas at different times. The engine air intake line is fluidly connected receive syngas from the syngas generator or depleted syngas exiting an exhaust after-treatment device or both.

In various systems and methods for reducing NOx levels in a combustion engine exhaust stream the system includes one or more catalytic lean NOx traps. A reducing agent (such as syngas) is produced in a reducing agent generator (such as a syngas generator). In a trapping mode, at least a portion of the engine exhaust stream is introduced into a catalytic lean NOx trap. In a regeneration mode syngas is introduced into the catalytic lean NOx trap to regenerate its capacity to trap NOx. Preferably the duration of the trapping mode is less than about 20 seconds. In preferred embodiments the duration of the regeneration mode is about the same as the duration of the trapping mode. For example, they can both be about 10 seconds. Preferably there is a pair of catalytic lean NOx traps in the system, and when one is in trapping mode the other is in regeneration mode.

The present systems that include a syngas generator (or other reducing agent generator) and one or more exhaust after-treatment devices permit operation of an engine system with improved fuel economy. Instead of being selected to reduce emissions, the timing of the fuel injection into the engine can be selected for improved fuel economy, but so that the level of regulated emissions in said engine exhaust stream might at least periodically exceeds regulation levels. For example, the NOx level in the exhaust stream from the engine may exceed regulation levels. However the exhaust stream is then directed to at least one exhaust after-treatment device in the engine exhaust after-treatment system, for reducing emissions from the engine below the regulated levels. The syngas stream is used to regenerate or heat the exhaust after-treatment devices as needed.

In the system and methods described above, the syngas generator is conveniently operated using a portion of the engine exhaust stream (as oxidant) and the same fuel that is used in the combustion engine as the fuel stream. These streams are converted to syngas in the syngas generated. In preferred embodiments the syngas generator is non-catalytic.

In the system and methods described above, an engine exhaust gas recirculation (EGR) system can be omitted. In other words, the system can be operated so that engine exhaust gas is not recirculated to the engine.

In preferred embodiments the system and methods described above the exhaust after-treatment system includes one or more lean NOx traps. It can instead, or in addition, comprise other after-treatment devices such as, for example, diesel particulate filters (DPFs or CDPFs), diesel oxidation catalysts (DOCs), and selective catalytic reduction (SCR) devices. The system design and method of operation of the SGG and associated components can be used to provide syngas for improved operation such devices. This is especially true during regeneration and when the device or engine is cold.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a process flow diagram of a representative conventional (prior art) diesel engine system that has been used in medium and heavy duty trucks and other such vehicles both on-road and off-road.

FIG. 2 is a schematic diagram illustrating the catalytic mechanisms involved in trapping and regeneration modes of typical LNTs.

FIG. 3 is a process flow diagram of a representative conventional (prior art) diesel engine system that employs catalysts and adsorbents to remediate the engine exhaust stream.

FIG. 4 is a process flow diagram of a first diesel engine system embodiment having an exhaust after-treatment module that employs syngas along with catalysts and adsorbents to remediate the engine exhaust stream.

FIG. 5 a is a process flow diagram of a second diesel engine system embodiment having an exhaust after-treatment module that employs syngas along with a pair of reciprocating LNTs containing catalysts and adsorbents to remediate the engine exhaust stream.

FIG. 5 b is simplified schematic diagram of a portion of the exhaust after-treatment module of the diesel engine system embodiment of FIG. 5 a.

FIG. 6 is a process flow chart illustrating a typical fuel conversion process in a SGG

FIGS. 7 a and 7 b illustrate a flow diverter employable in an exhaust after-treatment module of the present diesel engine system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

In preferred embodiments of the present approach, a combustion engine system incorporates a syngas generator (SGG), and syngas, is supplied to one or more parts of the engine system including the engine exhaust after-treatment system, resulting in reduced emissions and/or reduced fuel consumption. Preferred embodiments of the present system and method have at least several of the following features:

-   -   (a) A syngas generator (SGG) that receives diesel fuel and a         portion of the engine exhaust stream to produce a syngas stream         that contains H₂ and CO. The SGG can have a non-catalytic design         that employs a portion of the syngas sensible heat to preheat         the reactants (although the SGG can also operate without         performing this function).     -   (b) Passive control of the supply of oxidant (engine exhaust gas         stream) to the SGG.     -   (c) A metering pump to deliver diesel fuel from the primary         diesel fuel tank to the SGG. The metering pump supplies a         relatively low pressure stream that is sufficient, in         combination with other SGG components, to promote atomization         and then vaporization of the diesel fuel within the SGG. The         metering pump receives flow control signals from the engine         control module.     -   (d) One or more flow diverters to direct the syngas stream and         the engine exhaust stream to the appropriate emission control         device at the appropriate point of time in the engine operating         cycle. Syngas can be directed to some or all of the         after-treatment devices employed in the system.     -   (e) A lean NOx trap (LNT) system that employs two or more LNT         catalyst beds and that cycles quickly between the beds to         achieve greater adsorption and desorption rates than those         achievable with conventional, prior art systems.     -   (f) A catalyzed diesel particulate filter (CDPF) that can         optionally employ the syngas stream from the SGG. A CDPF traps         PM (soot or coke) in the exhaust stream and oxidizes the carbon         into CO or CO₂. The following chemical reactions occur in a         typical CDPF:         C+O₂═CO₂   (1)         C+½O₂═CO   (2)     -   The CDPF catalyst must generally be above a minimum temperature         for the oxidation process to occur. The higher the oxygen         concentration present the lower the temperature can be. During         various points in the engine operating cycle, the engine exhaust         may not be hot enough to heat the catalyst to the required         temperature. Syngas from the SGG can be introduced into the         CDPF, to react with the catalyst and raise the catalyst         temperature to the level required to oxidize the soot or coke.         In this regard, syngas does not directly promote the         regeneration of the CDPF. The primary purpose of using syngas in         the CDPF is as a fuel that can be burned to increase the         temperature of the CDPF to the point where oxidation of the         trapped carbon can take place. This is also the case with a         non-catalyzed DPF because, at high enough temperatures, the         syngas fuel will burn without a catalyst.     -   (g) A diesel oxidation catalyst device (DOC) for reducing the         level of CO and unburned hydrocarbon (HC) in the exhaust stream,         which can optionally employ syngas from the SGG to enhance the         effectiveness of the DOC during various points of time in the         engine operating cycle. In this regard, syngas can assist in         bringing the DOC quickly to proper operating temperature when         the engine is started, and thereby achieve greater exhaust         after-treatment efficiencies than those achievable with         conventional, prior art systems.     -   (h) Local and/or distributed engine control module hardware and         software for controlling the SGG and flow diverter operation         based on various engine operating parameters to achieve greater         exhaust after-treatment efficiencies, using less diesel fuel,         and in a more compact after-treatment module volume, than those         achievable with conventional, prior art systems.     -   (i) Engine control module software for adjusting (advancing)         fuel injection timing, thereby permitting improved engine fuel         economy and reduced PM levels, but increasing NOx content in the         engine exhaust stream which is then mitigated in the         after-treatment system.

(j) Directing the depleted syngas stream from the LNT regeneration step back to the engine air intake stream to make use of residual heating value remaining in the depleted syngas stream.

(k) Directing excess syngas (that is not needed for heating or regeneration of the exhaust after-treatment devices) back to the engine air intake stream, thereby allowing the syngas generator to operate continuously and at the same time making use of the heating value of the syngas stream produced.

In preferred embodiments of the system and method, conventional exhaust gas recirculation (EGR) components can be omitted, thereby reducing radiator heat load and also reducing costs. The resultant increase in NOx from the omission of EGR is remediated by the after-treatment system incorporating syngas generation.

In most countries there are emissions regulations in place that specify acceptable levels for specific constituents of engine exhaust streams that are harmful to human health or to the environment. The specific regulations and acceptable levels for each type of emission constituent vary depending upon the type of engine system involved, and also geographically depending on national or regional regulations. The regulations are also adjusted over time, generally becoming more and more stringent in global efforts to protect the environment.

Regulations related to emissions and air quality may generally be divided into two classes:

(A) “tailpipe” emission regulations;

(B) ambient air quality standards.

Diesel engines for highway applications and some for off-road use are subject to the “tailpipe” emission regulations. These regulations specify the maximum amount of pollutants allowed in exhaust gases from a diesel engine. The emissions are measured over an engine test cycle which is also specified in the regulations. The duty to comply is typically on the equipment (engine) manufacturer. The authorities regulating engine tailpipe emissions include the US EPA (Environmental Protection Agency) and California ARB (Air Resources Board). Many applications of diesel engines in confined spaces are regulated through ambient air quality standards rather than by tailpipe regulations. The ambient air quality standards specify the maximum concentrations of air contaminants which are allowed in the workplace. These regulations are set and enforced by occupational health and safety authorities such as OSHA (Occupational Health and Safety Administration) or MSHA (Mining Safety and Health Administration). The duty to comply is on the end-user who has to make sure that the emission control measures which have been employed are adequate.

As used herein, references to “regulated emissions” refer to pollutants that occur in engine exhaust streams that are typically regulated. These include NOx, CO, hydrocarbons, SO₂ and particulate matter (PM).

As used herein, references to improving fuel economy generally mean reducing the “brake specific fuel consumption” (BSFC) of the engine system. Fuel consumption mass per unit time is normally recorded during engine testing. One way to evaluate engine system efficiency is to look at the ratio of fuel consumption to useful power. This ratio is the BSFC which, in essence, is a measure of how much fuel an engine system consumes in the process of producing a specific horsepower output.

Turning now to FIG. 1, a representative conventional (prior art) diesel engine system 10 includes a combustion engine 12 having one or more combustion cylinders, one of which is denoted in FIG. 1 as cylinder 12 a. As shown, system 10 includes four subsystems or modules surrounding engine 12, namely:

a fuel intake module 14;

an air intake module 16;

an exhaust module 18; and

an engine control module 19.

As further shown in FIG. 1, fuel intake module 14 includes a diesel fuel tank 20, a fuel injection assembly 24 and a fuel conduit 22 fluidly connecting fuel tank 20 and fuel injection system 24. Diesel fuel is injected into each of the cylinders of engine 12 via injectors (the injected fuel is represented in FIG. 1 by conduit 25).

As further shown in FIG. 1, air intake module 16 includes an air inlet stream 30, through which air is introduced to air filter 32. Filtered air stream 34 exiting air filter 32 is directed to air flow sensor 36. Air stream 38 exiting air flow sensor 36 is directed to a compressor (shown in FIG. 1 as compressor portion 40 a of a turbocompressor, the turbine portion of which is shown as turbine portion 40 b in exhaust module 18). Air stream 42 exiting compressor portion 40 a is directed to an intake air cooler 44. Cooled air stream 46 exiting air intake cooler 44 is merged at junction valve 47 with a recirculated exhaust gas stream 68 (described in more detail below in connection with exhaust module 18). Merged air stream 48 is directed to air intake 50 of engine 12, where it is combusted along with fuel from injectors 25 in the cylinders of engine 12 to produce motive power.

As further shown in FIG. 1, exhaust module 18 includes an engine exhaust stream 52, which exits engine 12 at exhaust outlet 51. Exhaust stream 52 is directed to a two-way valve 53, through which at least a portion of exhaust stream 52 exits as recirculated exhaust gas stream 60, and the remaining portion of exhaust stream 52 exits valve 53 as exhaust stream 54. As shown in FIG. 1, exhaust stream 54 is directed from valve 53 to turbine portion 40 b of the turbocompressor, the compressor portion of which is shown in FIG. 1 as compressor portion 40 a of air intake module 16. The exhaust stream 56 exiting turbine portion 40 b is exhausted from exhaust module 18 to the external atmosphere through muffler and tail pipe assembly 94.

From valve 53 in FIG. 1, recirculated exhaust gas stream 60 is directed through exhaust gas recirculation (EGR) cooler 62, as cooled exhaust gas stream 64, to an EGR valve 66. Recirculated exhaust gas stream 68 exiting EGR valve 66 is directed to junction valve 47, where stream 68 is merged with air stream 46 to produce merged air stream 48.

As further shown in FIG. 1, engine control module 19 includes a microprocessor 96 that receives electronic signals (denoted in FIG. 1 by the arrows extending toward the letter “S”) from engine 12, fuel tank 20, and air flow sensor 36. Microprocessor 96 directs signals (denoted in FIG. 1 by the arrows extending away from the letter “S”) to engine 12 (double-headed arrows indicate that microprocessor 96 directs signals to and receives signals from engine 12). Microprocessor 96 also directs signals to the turbocompressor (namely, to compressor portion 40 a and to turbine portion 40 b), as well as to fuel injector assembly 24.

FIG. 2, showing the catalytic mechanisms involved in trapping and regeneration modes of typical LNTs, is described in the Background of the Invention section above.

Turning now to FIG. 3, a representative conventional (prior art) diesel engine system 110, which employs catalysts and adsorbents to remediate the engine exhaust stream, includes a combustion engine 112 having one or more combustion cylinders, one of which is denoted in FIG. 3 as cylinder 112 a. As shown, system 110 includes four subsystems or modules surrounding engine 112, namely:

a fuel intake module 114;

an air intake module 116;

an exhaust after-treatment module 118; and

an engine control module 119.

Fuel intake module 114 of FIG. 3 is substantially identical in configuration to fuel intake module 14 of FIG. 1. As shown in FIG. 3, fuel intake module 114 includes a fuel tank 120, a fuel injection assembly 124 and a fuel conduit 122 fluidly connecting fuel tank 120 and fuel injection system 124. Fuel is injected into each of the cylinders of engine 112 via injectors (the injected fuel is represented in FIG. 3 by conduit 125).

Air intake module 116 of FIG. 3 is substantially identical in configuration to air intake module 16 of FIG. 1. As shown in FIG. 3, air intake module 116 includes an air inlet stream 130, through which air is introduced to air filter 132. Filtered air stream 134 exiting air filter 132 is directed to air flow sensor 136. Air stream 138 exiting air flow sensor 136 is directed to a compressor (shown in FIG. 3 as compressor portion 140 a of a turbocompressor, the turbine portion of which is shown as turbine portion 140 b in exhaust after-treatment module 118). Air stream 142 exiting compressor portion 140 a is directed to an intake air cooler 144. Cooled air stream 146 exiting air intake cooler 144 is merged at junction valve 147 with a recirculated exhaust gas stream 168 (described in more detail below in connection with exhaust after-treatment module 118). Merged air stream 148 is directed to air intake 150 of engine 112, where it is combusted along with fuel from injectors 125 in the cylinders of engine 112 to produce motive power.

As further shown in FIG. 3, exhaust after-treatment module 118 includes an engine exhaust stream 152, which exits engine 112 at exhaust outlet 151. Exhaust stream 152 is directed to a two-way valve 153, through which at least a portion of exhaust stream 152 exits as recirculated exhaust gas stream 160, and the remaining portion of exhaust stream 152 exits as exhaust stream 154. As shown in FIG. 3, exhaust stream 154 is directed from valve 153 to turbine portion 140 b of the turbocompressor, the compressor portion of which is shown in FIG. 3 as compressor portion 140 a of air intake module 116. The exhaust stream 156 exiting turbine portion 140 b is directed to catalyzed diesel particulate filter (CDPF) 170, where particulate matter (including soot and carbon particles) is removed from exhaust stream 156 to produce a filtered exhaust stream 174. Filtered exhaust stream 174, is directed to NOx reduction device 176, to convert at least some of the NOx compounds present in exhaust stream 174 to benign nitrogen constituents, including N₂. Fuel from fuel stream 173 and drawn from fuel tank 120, is injected into exhaust stream 174, as required to regenerate NOx reduction device 176, namely, a lean NOx trap (LNT) or a NOx adsorber. Exhaust stream 178 exiting NOx reduction device 176 is directed to diesel oxidation catalyst (DOC) device 180, where the following reactions occur: Hydrocarbons+O₂═CO₂+H₂O   (1) CO+½O₂═CO₂   (2) thereby converting hydrocarbons (HC) and CO present in exhaust stream 178 to CO₂ and H₂O. The DOC employs catalysts such as platinum to promote the oxidation of unburned HCs and CO with O₂ in the exhaust stream. Exhaust stream 182 exiting DOC 180 is exhausted from exhaust after-treatment module 118 to the external atmosphere through muffler and tail pipe assembly 194.

From valve 153 in FIG. 3, recirculated exhaust gas stream 160 is directed through EGR cooler 162, as cooled exhaust gas stream 164, to an EGR valve 166. Recirculated exhaust gas stream 168 exiting EGR valve 166 is directed to junction valve 147, where stream 168 is merged with air stream 146 to produce merged air stream 148.

As further shown in FIG. 3, engine control module 119 includes a microprocessor 196 that receives electronic signals from engine 112, fuel tank 120, and air flow sensor 136. Microprocessor 196 directs signals to engine 112, compressor portion 140 a, turbine portion 140 b, and fuel injector assembly 124.

In system 110 of FIG. 3, the engine control module 119 sends a signal to control fuel stream 173 so that, at a programmed interval, a programmed amount of hydrocarbon fuel is introduced into exhaust stream 174. Heat from the engine exhaust vaporizes the fuel as it flows into NO_(x) reduction device 176. The oxygen in the engine exhaust is combusted into CO₂ and H₂O over the oxidation catalyst creating a fuel-rich condition that regenerates the NO_(x) reduction device 176. A difference between system 10 of FIG. 1 and system 110 of FIG. 3 is that exhaust module 118 of FIG. 3, contains various exhaust after-treatment devices (such as NO_(x) reduction device 176, CDPF 170, and DOC 180) to reduce undesirable emissions from system 110. In particular, in operation of system 110 some of the fuel that is also used in the engine is injected directly into the engine exhaust stream to regenerate NO_(x) reduction device 176, as required. There is an estimated fuel economy penalty of 3-5% in operating this system. System 10 of FIG. 1, does not contain such an exhaust after-treatment system, but it will generate higher levels of regulated emissions.

Turning now to FIG. 4, a diesel engine system 210 has an exhaust after-treatment module 218 that employs syngas along with catalysts and adsorbents to remediate the engine exhaust stream. System 210 of FIG. 4 also employs exhaust gas recirculation (EGR). System 210 includes a combustion engine 212 having one or more combustion cylinders, one of which is denoted in FIG. 4 as cylinder 212 a. As shown, system 210 includes four subsystems or modules surrounding engine 212, namely:

a fuel intake module 214;

an air intake module 216;

an exhaust after-treatment module 218, incorporating a syngas generator 263; and

an engine control module 219.

Fuel intake module 214 of FIG. 4 is substantially identical in configuration to fuel intake module 14 of FIG. 1 and fuel intake module 114 of FIG. 3. As shown in FIG. 4, fuel intake module 214 includes a diesel fuel tank 220, a fuel injection assembly 224 and a fuel conduit 222 fluidly connecting fuel tank 220 and fuel injection system 224. Diesel fuel is injected into each of the cylinders of engine 212 via injectors (the injected fuel is represented in FIG. 4 by conduit 225).

Air intake module 216 of FIG. 4 is substantially identical in configuration to air intake module 16 of FIG. 1 and air intake module 116 of FIG. 3. As shown in FIG. 4, air intake module 216 includes an air inlet stream 230, through which air is introduced to air filter 232. Filtered air stream 234 exiting air filter 232 is directed to air flow sensor 236. Air stream 238 exiting air flow sensor 236 is directed through a venturi 239 to a compressor (shown in FIG. 4 as compressor portion 240 a of a turbocompressor, the turbine portion of which is shown as turbine portion 240 b in exhaust after-treatment module 218). Air stream 242 exiting compressor portion 240 a is directed to an intake air cooler 244. Cooled air stream 246 exiting air intake cooler 244 is merged at junction valve 247 with a recirculated exhaust gas stream 268 (described in more detail below in connection with exhaust after-treatment module 218). Merged air stream 248 is directed to air intake 250 of engine 212, where it is combusted along with fuel from injectors 225 in the cylinders of engine 212 to produce motive power.

As further shown in FIG. 4, exhaust after-treatment module 218 includes an engine exhaust stream 252, which exits engine 212 at exhaust outlet 251. Exhaust stream 252 is directed to a two-way valve 255 through which at least a portion of exhaust stream 252 exits as exhaust slip stream 252 a, and the remaining portion of exhaust stream 252 exits valve 255 as exhaust stream 252 b.

Exhaust slip stream 252 a is directed to a syngas generator (SGG) 263. A diesel fuel stream 273 is drawn from fuel tank 220 via metering pump 223 and is also directed to SGG 263. SGG 263 includes a mixing zone, an oxidizing zone and a reforming zone (as described in more detail below in connection with FIG. 6). Diesel fuel from stream 273 is atomized and then vaporized in the SGG mixing zone, and is then combusted in the SGG oxidizing zone with oxygen present in exhaust slip stream 252 a to produce, in the SGG reforming zone, a syngas stream 265 containing H₂ and CO. Syngas stream 265 is directed to a syngas flow diverter 284, where the syngas stream is selectively directed via branched streams to downstream after-treatment module components, including catalyzed diesel particulate filter (CDPF) 270, NOx reduction device 276, and diesel oxidation catalyst (DOC) device 280, as will be described in more detail below.

As further shown in FIG. 4, exhaust stream 252 b exiting two-way valve 255 is directed to a two-way valve 253, through which at least a portion of exhaust stream 252 b exits valve 253 as recirculated exhaust gas stream 260 (and is recirculated via an EGR loop as described below), and the remaining portion of exhaust stream 252 exits as exhaust stream 254. As shown in FIG. 4, exhaust stream 254 is directed from valve 253 to turbine portion 240 b of the turbocompressor, the compressor portion of which is shown in FIG. 4 as compressor portion 240 a of air intake module 216.

Exhaust stream 256 exiting turbine portion 240 b is directed to CDPF 270, where particulate matter (including soot and carbon particles) is removed from exhaust stream 256 to produce a filtered exhaust stream 274. A branch syngas stream 286 is directed from syngas diverter 284 to CDPF 270 to promote operation of the CDPF 270, as described above.

Filtered exhaust stream 274 is directed to NOx reduction device 276 (which can be an LNT) to convert at least some of the NOx compounds present in exhaust stream 274 to benign constituents, primarily N₂, H₂O and CO₂. A branch syngas stream 290 is directed from syngas diverter 284 to LNT 276 to promote regeneration of adsorbent within LNT 276, as described above.

As further shown in FIG. 4, exhaust stream 278 exiting LNT 276 is directed to diesel oxidation catalyst (DOC) device 280, where HC and CO present in exhaust stream 278 are converted to more environmentally benign reaction products, primarily H₂O and CO₂. In addition, a branch syngas stream 293 is directed from syngas diverter 284 to DOC 280 to react with and heat the catalyst in the DOC to the desired operating temperature.

Exhaust stream 282 exiting DOC 280 is exhausted from exhaust after-treatment module 218 to the external atmosphere through tail pipe 294.

Excess syngas stream 288 (that is not directed to the various after-treatment module components) is directed from syngas diverter 284 back to engine air intake module 216. Rather than being directed to the engine air intake module 216 via the EGR loop, in the illustrated embodiment syngas stream 288 is directed to a venturi 239 located upstream of compressor portion 240 a, where it is drawn into and merged with air stream 238 exiting air flow sensor 236. Excess syngas stream 288 can be directed through one or more filters or traps such as particulate filters or sulfur traps, (not shown in FIG. 4), located between syngas diverter 284 and venturi 239. In alternative embodiments the excess syngas stream can be introduced into the engine air intake stream downstream of the compressor.

From valve 253 in FIG. 4, recirculated exhaust gas stream 260 is directed through EGR cooler 262, as cooled exhaust stream 264, to an EGR valve 266. Recirculated exhaust gas stream 268 exiting EGR valve 266 is directed to junction valve 247, where stream 268 is merged with air stream 246 to produce merged air stream 248.

As further shown in FIG. 4, exhaust after-treatment module 218 includes a local control module 298, which receives electronic signals from engine 212, fuel tank 220, SGG 263, CDPF 270, LNT 276, DOC 280 and engine control module 219. Exhaust after-treatment control module 298, controls the operation of the SGG 263, based on pre-programmed algorithms based on one or more system operating parameters, such as NOx concentration after the LNT, O₂ content in stream exiting the LNT, engine speed, temperature, fuel injection timing, air intake mass flow, accelerator or throttle position, duration and fuel pressure. Exhaust after-treatment control module 298 determines the regeneration requirements and operating condition of the after-treatment devices based on signals received from those devices. Exhaust after-treatment control module 298, directs the appropriate signals to metering pump 223 and flow diverter 284, controlling the production of syngas and the flow of the syngas to the appropriate after-treatment device(s) when required.

Engine control module 219 includes a microprocessor 296 that receives electronic signals from engine 212, fuel tank 220, air flow sensor 236 and local control module 298. Microprocessor 296 directs signals to engine 212, fuel injector assembly 224, compressor portion 240 a, turbine portion 240 b, SGG 263 and EGR valve 266.

In prior art system 110 of FIG. 3, in order to regenerate NOx reduction device 176, fuel from fuel tank 120 is introduced directly into the engine exhaust stream 174 upstream of the device 176. This creates a rich environment that regenerates device 176. This in-situ production of reducing agent is intermittent and only as required to regenerate the device 176. However, the process of converting the fuel to a reducing agent in-situ is inefficient, resulting in excess fuel consumption and the formation of undesired by-products such as soot. In contrast, in system 210 of FIG. 4, the fuel is first converted to syngas in SGG 263 and the syngas is then directed to the various exhaust after-treatment devices (CDPF 270, LNT 276 and/or DOC 280) as required for regeneration or heating. Excess syngas is diverted to the engine air intake module 216 via a dedicated line, to be consumed by the engine. The SGG 263, may be operated continuously while the engine is on. This can reduce thermal stresses associated with starting and stopping operating of the SGG. Preferred methods of operating the SGG continuously in such a system are described in co-pending United States Provisional Patent Application Ser. No. 60/890,600 filed on Feb. 19, 2007, entitled “Method Of Operating A Syngas Generator”.

Turning now to FIG. 5 a, a diesel engine system 310 has an exhaust after-treatment module 318 that employs syngas along with a pair of reciprocating lean NOx traps containing catalysts and adsorbents to remediate the engine exhaust stream. System 310 of FIG. 5 a does not employ exhaust gas recirculation (EGR). System 310 includes a combustion engine 312 having one or more combustion cylinders, one of which is denoted in FIG. 5 a as cylinder 312 a. As shown, system 310 includes four subsystems or modules surrounding engine 312, namely:

-   -   a fuel intake module 314;     -   an air intake module 316;     -   an exhaust after-treatment module 318 incorporating a syngas         generator 363; and     -   an engine control module 319.

Fuel intake module 314 of FIG. 5 a is substantially identical in configuration to fuel intake module 14 of FIG. 1, fuel intake module 114 of FIG. 3, and fuel intake module 214 of FIG. 4. As shown in FIG. 5 a, fuel intake module 314 includes a diesel fuel tank 320, a fuel injection assembly 324 and a fuel conduit 322 fluidly connecting fuel tank 320 and fuel injection system 324. Diesel fuel is injected into each of the cylinders of engine 312 a via injectors (the injected fuel is represented in FIG. 5 a by conduit 325).

Air intake module 316 of FIG. 5 a is substantially identical in configuration to air intake module 16 of FIG. 1, air intake module 116 of FIG. 3, and air intake module 216 of FIG. 4. As shown in FIG. 5 a, air intake module 316 includes an air inlet stream 330, through which air is introduced to air filter 332. Filtered air stream 334 exiting air filter 332 is directed to air flow sensor 336. Air stream 338 exiting air flow sensor 336 is directed through a venturi 339 to a compressor (shown in FIG. 5 a as compressor portion 340 a of a turbocompressor, the turbine portion of which is shown as turbine portion 340 b in exhaust after-treatment module 318). Air stream 342 exiting compressor portion 340 a is directed to an intake air cooler 344. Cooled air stream 346 exiting air intake cooler 344 is directed to air intake 350 of engine 312, where it is combusted along with fuel from injectors 325 in the cylinders of engine 312 to produce motive power.

Exhaust after-treatment module 318 includes an engine exhaust stream 352, which exits engine 312 at exhaust outlet 351. Exhaust stream 352 is directed to a two-way valve 355 through which at least a portion of exhaust stream 352 exits as exhaust slip stream 352 a, and the remaining portion of exhaust stream 352 exits valve 355 as exhaust stream 352 b. Exhaust stream 352 b exiting two-way valve 355 is directed to turbine portion 340 b of the turbocompressor, the compressor portion of which is shown in FIG. 5 a as compressor portion 340 a of air intake module 316. Exhaust stream 356 exiting turbine portion 340 b is directed to catalyzed diesel particulate filter (CDPF) 370, where particulate matter (including soot and carbon particles) is removed from exhaust stream 356 to produce a filtered exhaust stream 374. Filtered exhaust stream 374 is then directed to the exhaust stream inlet of an upstream flow diverter 367.

Referring now to FIG. 5 b (which is simplified schematic diagram of a portion of the exhaust after-treatment module 318), as well as to FIG. 5 a, exhaust slip stream 352 a is directed to a syngas generator (SGG) 363. A diesel fuel stream 373 drawn from fuel tank 320 via metering pump 323 is also directed to SGG 363. SGG 363 includes a mixing zone, an oxidizing zone and a reforming zone (as described in more detail below in connection with FIG. 6). Diesel fuel stream 373 is atomized and then vaporized in the SGG mixing zone, and is then oxidized in the SGG oxidizing zone with oxygen present in exhaust slip stream 352 a to produce, in the SGG reforming zone, a syngas stream 365 containing H₂ and CO. Syngas stream 365 is directed to the syngas stream inlet of an upstream flow diverter 367.

In a first mode, upstream flow diverter 367 directs exhaust stream 374 to a first upstream conduit 369 a, which is connected at its distal end to the inlet of a first lean NOx trap (LNT) 371 a. While in the first mode, upstream flow diverter 367 also directs syngas stream 365 to a second upstream conduit 369 b, which is connected at its distal end to the inlet of a second LNT 371 b. In the first mode, LNT 371 a is in trapping (lean) mode, while LNT 371 b is in regeneration (rich) mode (see FIG. 2 and description).

In a second mode (which is the mode illustrated in FIG. 5 b), upstream flow diverter 367 directs exhaust stream 374 to second upstream conduit 369 b, which is connected at its distal end to the inlet of second LNT 371 b. While in the second mode, upstream flow diverter 367 also directs syngas stream 365 to first upstream conduit 369 a, which is connected at its distal end to the inlet of second LNT 371 a. In the second mode, LNT 371 b is in trapping (lean) mode, while LNT 371 a is in regeneration (rich) mode.

As directed by control software, upstream flow diverter 367 periodically redirects these two streams to the opposing LNTs such that each of LNT 371 a and 371 b cycles between a trapping mode and a regeneration mode. Upstream flow diverter 367 is thus employed to simultaneously direct the engine exhaust stream and the syngas stream. This dual functionality of the flow diverter reduces system cost and size/volume.

As further shown in FIGS. 5 a and 5 b, a first downstream conduit 373 a fluidly connects the outlet of LNT 371 a to a first inlet 376 a of a downstream flow diverter 375. A second downstream conduit 373 b fluidly connects the outlet of LNT 371 b to a second inlet 376 b of a downstream flow diverter 375.

When LNT 371 a is in trapping mode, downstream flow diverter 375 directs the treated exhaust stream exiting LNT 371 a to an exhaust outlet conduit 378, which is fluidly connected at its distal end to a DOC device 380. When LNT 371 a is in regeneration mode, downstream flow diverter 375 directs the syngas stream exiting LNT 371 a to a depleted syngas conduit 388, which is fluidly connected at its distal end to venturi 339, where depleted syngas stream 388 is merged with air stream 338.

When LNT 371 b is in trapping mode, downstream flow diverter 375 directs the treated exhaust stream exiting LNT 371 b to exhaust outlet conduit 378. When LNT 371 b is in regeneration mode, downstream flow diverter 375 directs the syngas stream exiting LNT 371 b to depleted syngas conduit 388.

The depleted syngas stream that flows to intake valve (venturi) 339 passes through a sulfur trapping bed 377. Sulfur components from the engine exhaust stream tend to accumulate in the LNTs, particularly near the inlet. In the regeneration of the LNTs, these sulfur components are released, primarily as hydrogen sulfide (H₂S). Sulfur trapping bed 377 removes at least some of the sulfur components from the depleted syngas stream, and thereby inhibits sulfur from accumulating due to the recycling of syngas. The depleted syngas stream may also be directed through one or more particulate filters or other types of traps or filters that could be part of bed 377 or could be separate devices.

As further shown in FIG. 5 a, exhaust stream 378 exiting downstream flow diverter 375 is directed to DOC device 380, where HC and CO present in exhaust stream 378 are converted to more environmentally benign reaction products H₂O and CO₂. Exhaust stream 382 exiting DOC 380 is exhausted from exhaust after-treatment module 318 to the external atmosphere through a tail pipe (not shown in FIG. 5 a).

As further shown in FIG. 5 a, engine control module 319 includes a microprocessor 396 that receives electronic signals from engine 312, fuel tank 320, and air flow sensor 336. Microprocessor 396 directs signals to engine 312, metering pump 323, fuel injector assembly 324, compressor portion 340 a, turbine portion 340 b, and SGG 363.

In the embodiment illustrated in FIG. 5 a, the system does not include an exhaust gas recirculation (EGR) line and associated components.

Omission of the EGR components from system 310 in FIG. 5 a has the following benefits:

-   -   (a) Engine system cost is reduced.     -   (b) Engine system complexity and weight is reduced.     -   (c) Particulate matter (PM) levels in the engine exhaust are         reduced, thereby imposing less of a burden on the PM reduction         system (for example, the DPF requires regeneration less         frequently).     -   (d) Reduction of cooling load on the radiator, which represents         an especially valuable benefit in view of the reduced frontage         size of the hood and associated radiator cooling capacity of         over-the-road diesel engine trucks and tractors.     -   (e) The reduction in the engine system operating temperature         caused by the elimination of the EGR can improve system         reliability and durability, by increasing the operating life of         various system components.

In a preferred system, the engine combustion process can be tailored for high fuel economy rather than making a compromise that yields lower NOx levels. An increase in the NOx levels as a result of removing the EGR system can be compensated for in the NOx removal system (for example, the LNT system), which is designed specifically for removing NOx. The presence of the NOx removal system in the present design avoids the traditional compromise between engine design parameters when seeking both production of motive power efficiently and reduction of engine exhaust pollutants.

In preferred embodiments of the present system, the SGG receives diesel fuel and a portion of the engine exhaust stream to produce a syngas stream that contains H₂ and CO. In preferred embodiments, a small portion of the engine exhaust stream is drawn at a point between the engine exhaust manifold and the turbine inlet, and then directed to a SGG via a process line. The high temperature and pressure of the exhaust stream drawn at this point is desirable for the operation of the downstream SGG. The syngas process line is designed to discourage heat loss, discourage pressure drop, reduce cost and facilitate packaging. Keeping the syngas process line short in length and large in diameter mitigates pressure drop and heat loss and eases packaging. The syngas process line is insulated to further mitigate heat loss. Again, this is done because high temperature and pressure benefit the downstream SGG. The syngas process line preferably does not include control devices, as they act as heat sinks, make packaging more difficult and add cost.

A portion of the engine exhaust stream is employed as a reactant feed for the SGG primarily because of the oxygen, water, and carbon dioxide content of the stream, which are all useful in the production of syngas. A secondary benefit of employing the engine exhaust gas stream is for its sensible heat content. Employing a portion of the engine exhaust stream as a reactant avoids the need for an oxygen or water supply subsystem that would add cost, volume, weight and complexity to the overall engine and vehicle product.

Diesel fuel is drawn from the on-board diesel fuel tank by a metering pump. This may involve typical equipment such as fuel filters. The metering pump typically has an accuracy of better than ±20% of flow, as this accuracy balances a trade-off between cost and stability, as well as ability to meet requirements of the after-treatment system. The discharge flow rate of the pump is commanded by the engine control module and its software, based on algorithms specific to the application. The metering pump discharge pressure is typically between 3 and 50 psig. This pressure is suitable for the downstream mixing of the two streams in the SGG.

The diesel fuel metering pump is preferably placed in a position so that the diesel fuel temperature range due to ambient temperature fluctuations is minimized or reduced. The pump could be positioned directly next to the diesel fuel tank. A minimal or reduced diesel fuel temperature swing permits more accurate metering of the diesel fuel.

In preferred embodiments, the downstream flow diverter simultaneously directs the depleted syngas stream exiting the LNT in the regenerating mode to the engine air intake line to capture and combust in the engine the fuel value remaining in the depleted syngas stream. The depleted syngas stream conduit is preferably positioned to join the air intake line at a point directly upstream of the compressor (as shown in FIG. 5 a described above), although it could be connected at a different point relative to the compressor. A venturi device placed in the air intake line assists in the flow of excess syngas or depleted syngas from the after-treatment system to the air intake line. The ability of the present system to direct excess syngas or depleted syngas to the air intake line has the following benefits:

-   -   (a) The syngas flow rate to the LNT during regeneration can be         increased so that the regeneration is faster and more complete,         yet additional syngas is not directed to the tailpipe but is         directed back to the engine to capture its fuel value.     -   (b) Ability to reduce the required turndown ratio of the SGG by         keeping the SGG operating even when syngas is not required, or         when only small quantities are required.     -   (c) Ability to increase engine output power on demand by         producing syngas for the express purpose of increasing engine         power and directing the syngas to the engine via the air intake         stream.

In order to illustrate the processes typical in a syngas generator, in which both partial oxidation and reforming reactions take place, FIG. 6 illustrates the main processes occurring in the conversion of a hydrocarbon fuel and an engine exhaust stream into a syngas stream in a partial oxidation fuel reformer. Syngas production can be segregated into three main processes: mixing, oxidizing and reforming, as shown in FIG. 6. The first process is the mixing process and it generally takes place at or near the inlet, where the engine exhaust stream and hydrocarbon fuel are introduced into the SGG, in the so-called “mixing zone”. The primary function of the mixing process is to supply an evenly mixed and distributed fuel-exhaust gas mixture for subsequent reactions. If the fuel is a liquid it is typically atomized and vaporized as well as being mixed with engine exhaust gas stream in this zone. The next process, the partial oxidation process, takes place downstream of the mixing zone, in the so called “combustion zone”. The primary function of this oxidation process is to ignite a portion of the fuel-oxidant mixture under fuel rich or sub-stoichiometric conditions to produce H₂ and CO as primary products as well as the sensible heat required for the downstream endothermic reformation reactions. This can be achieved by catalytically reacting and/or combusting the fuel with the oxygen in the engine exhaust stream. The final process, the reforming process, is where the partial oxidation products and remaining fuel constituents are further converted to hydrogen and carbon monoxide via reactions typical of reformation processes. The syngas then exits the SGG. There is not strict separation between the zones; rather the zones transition or merge into one another, but the primary processes happening in each of the zones are as described above. The fuel can be metered prior to the introduction into the SGG. If the fuel is in a liquid state, the fuel is atomized into droplets, vaporized and mixed with the engine exhaust gas stream—these processes typically occur upstream of and within the mixing zone. The sensible heat in the exhaust gas stream and high gas velocity facilitate fuel vaporization. Increased fuel vaporization improves the mixing of the fuel and engine exhaust stream. If the fuel source is in a gaseous state, it can merely be metered and mixed with the exhaust gas stream. In either case, the high shear stress created between the fuel and exhaust gas flows provides mixing of the two streams.

FIGS. 7 a and 7 b are cross-sectional views of a flow diverter, suitable for use in the present system, representing the flow diverter in two positions. The flow diverter comprises a single unsealed port 401, body 402, arm 403, valve 404, valve 405, sealable port 406, and sealable port 407. The flow diverter may be configured in such a manner that gases may enter the flow diverter from port 401 and exit through port 406 or port 407 or through a combination of port 406 and port 407. Alternatively, the flow diverter may be configured so that gases may enter the flow diverter from port 406 or port 407 or from a combination of port 406 and port 407 and exit through port 401. Port 406, and port 407, can be sealed one at a time by valves 404 and valves 405, which are mounted on a common pivoting actuating arm 403. Pivoting arm 403 may be actuated by an electrical motor or an electrical actuator (both not shown in FIGS. 7 a and 7 b). In the position shown in FIG. 7 a, gas flow through port 406 is blocked by valve 404. Gases are allowed to flow through port 401 and port 407. In FIG. 7 b, arm 403 is actuated to a position where valve 405 seals off the flow of gases through port 407. Gases are allowed to flow through port 401 and port 406.

Mode of Operation

Diesel engine embodiments of the present system are operated in a manner similar to that of conventional diesel engines. Each diesel engine has its own characteristics for the various engine system parameters over the engine application duty cycle. For example, the engine exhaust pressure and temperature will change depending on engine speed, torque, the engine control module calibration being used and to a lesser degree also with the engine life. Table 1 below provides an example of performance data for a specific engine, engine control module, engine control module calibration and application duty cycle. The after-treatment system is then designed and operated based on this data to achieve reduced exhaust emissions and improved fuel economy. TABLE 1 Performance data for a specific engine, engine control module calibration and application duty cycle. Throttle Position 55.1 100.1 42.8 Dyno/Engine Speed rev/min 1756.9 1756.8 1199.9 Dry Air-Fuel Ratio (r/r) 38.1 24.2 29.9 Intake Air Pressure kPa 99.5 97.2 100.6 Intake Air Temperature ° C. 15.5 16.7 16.1 Compressor Outlet Temperature ° C. 87.0 168.0 58.7 Diesel Fuel Mass Flow kg/h 25.3 74.5 19.9 Engine EGR Rate 21.2 16.9 16.0 (Wet CO2 Balance) Turbine Outlet Temperature ° C. 356.9 456.4 368.7 Exhaust Mass Flow (WPT) kg/h 998.1 1896.8 619.7

A significant aspect of the control and operation of the present diesel engine exhaust after-treatment system is the advancing of the fuel injection timing on the order of 3 crank angle degrees to 6 crank angle degrees compared to what is conventionally employed. These figures apply to the specific engine and engine configuration described here, and could vary in other engine configurations and end-uses. In the past, the fuel injection timing has generally been set so as to decrease NOx levels in the engine exhaust stream for the purpose of meeting NOx regulations. An undesirable side effect of this conventional timing protocol has been decreased fuel economy. While engine manufacturers constantly attempt to increase fuel economy, the need to meet ever more stringent NOx emission regulations has resulted in fuel injection timing that significantly reduces fuel economy. When fuel injection timing is advanced, the NOx levels in the exhaust stream are increased by approximately 10% to 50%. The additional NOx levels can be handled in the LNT portion of the present after-treatment system, and although diesel fuel is required to produce syngas for the LNT portion, this fuel penalty is more than off-set by the fuel savings due to advancing the fuel injection timing, so that the net result is a 3-10% reduction in total fuel consumption.

Significant aspects of preferred operating mode and control system embodiments are as follows:

-   -   (a) There is no active control of the oxidant supply (a small         portion of the engine exhaust stream) to the SGG. The SGG         oxidant flow is passively controlled and the turndown ratio is         limited due to a critical flow venturi that is part of the SGG,         and through which the fuel and exhaust gas are directed into the         SGG. As the engine exhaust pressure and temperature changes with         the engine duty cycle there will be changing mass flow through         the critical flow venturi, but the flow range will be smaller         than if a non-critical flow device was used. This method reduces         the cost of the system.     -   (b) The critical flow venturi is sized so as to give an         appropriate amount of oxidant, taking into account the changing         composition of the oxidant over the duty cycle, that will allow         production of syngas in the quantity required to reduce engine         exhaust NOx to regulated levels given the after-treatment system         used. This method of control is less expensive than methods         previously used.     -   (c) Diesel fuel flow to the SGG is controlled by the engine         control module commanding the metering pump to rotate at a speed         so as to give an appropriate fuel-oxidant ratio. Thus the diesel         fuel flow is controlled so that when it reacts in the SGG with         the oxidant flowing through the critical flow venturi it will         yield an appropriate amount of syngas to reduce engine exhaust         NOx to regulated levels given the after-treatment system used,         and keep the SGG internal temperatures at appropriate         temperatures (for example, 1000° C. to 1200° C.).

Thus, the syngas generator preferably uses a portion of the engine exhaust stream as an oxidant. The quantity of oxidant required by the syngas generator typically depends on the following parameters:

-   -   (a) The O₂, H₂O and CO₂ content.     -   (b) The rate at which the various after-treatment devices are         regenerated using the syngas, for example, the rate at which NOx         is removed from the LNTs during regeneration.     -   (c) The quantity of regulated emissions (for example, NOx) in         the engine exhaust, and the capacity of the after-treatment         system to trap such emissions.     -   (d) Aspects of the syngas generator design and operation such as         operating temperature and internal heat exchange.

In some embodiments of a system with dual LNTs, the control system monitors the duration that a LNT has been in trapping mode and then compares that to a predication/estimate of the NOx on the bed based on monitoring the duty cycle of the vehicle. Based on this comparison, the controller actuates the two flow diverters and thus changes the operating mode of each trap.

In the present approach, the LNT beds are in trapping mode preferably for only about 20 seconds or less, which is shorter than conventional trapping (adsorption) times. Furthermore, they are preferably regenerated for a period in the range of 5 to 20 seconds. The duration of this regeneration step is longer than is typical, and promotes the removal of sulfur compounds that accumulate in the bed (see below for more description of the sulfation problem). It can reduce or eliminate the need for a specific longer duration desulfating cycle. Thus, in the present approach the duration of the regeneration mode and the trapping mode are preferably about the same, thus the beds are preferably cycled at a rate in the order of once every 5 to 20 seconds. This cycling frequency is significantly greater than conventional. The faster cycling rate limits the amounts of NOx and sulfur adsorbed and allows for smaller and thus less expensive LNTs. Conventionally most LNT beds are operated in a regenerating mode for only a few seconds, with the trapping mode being substantially longer (often more than an order of magnitude longer than the regenerating mode).

Sulfur compounds tend to accumulate in LNTs particularly in the region near where the engine exhaust stream enters the trap. Sulfation of the trap over time tends to reduce its capacity to trap NOx, but desulfation of the trap generally requires high temperature treatment which can also be detrimental to the trap. Furthermore, during regeneration of the trap the sulfur compounds are converted to H₂S which absorbs preferentially over NO₂, and can further reduce the capacity of the trap. The present approaches described above, namely (a) using syngas, rather than diesel fuel, to regenerate the LNTs, and/or (b) using a shorter than conventional trapping times, and/or (c) using longer than conventional regeneration times, all facilitate desulfation. Nonetheless sulfation can still be a concern. One or more of following approaches can be used to further mitigate the problem:

-   -   (a) Three LNTs could be arranged in parallel, where two of them         are cycling quickly (for example, 5-20 seconds per trapping and         regeneration cycle) and these two are in opposite phase to each         other. The third LNT would be in a longer-duration desulfating         cycle (for example, in the range of 1 to 10 minutes). This would         allow two beds to operate normally while one bed can take the         time to be desulfated without disturbing the operation of the         two beds that are reducing engine exhaust stream NOx levels.     -   (b) During the regeneration step, the syngas could be directed         to flow in reverse (opposite to the direction that the engine         exhaust stream flowed) through the LNT. In this way, the sulfur         components which accumulated and are now liberated nearer to the         engine exhaust inlet, are removed directly from the bed, rather         than flowing through the length of the bed. This can reduce         sulfur poisoning of the major portion of the LNT.     -   (c) During the regeneration step, the syngas could be directed         to flow in reverse through the LNT as described above, but could         enter the trap at some point in the LNT bed beyond the location         at which the significant sulfur accumulation has occurred.     -   (d) The “front” portion of the LNT (near the engine exhaust         stream inlet) could have a different catalyst/adsorbent         formulation to assist in promoting desulfation.     -   (e) An electrical heater could be placed around the front         portion of the LNT and activated to increase bed temperature         during desulfation.     -   (f) Fuel could be burned to heat the front portion of the bed         just prior to supplying syngas in reverse flow for regeneration         or desulfation.     -   (g) Syngas and engine exhaust could be combusted in the bed         itself to provide heat for desulfating.) This could be done with         a slow switch-over of the diverter valves alone where the slow         movement of the valve allows mixing of the syngas with the         exhaust stream over the catalyst, thereby producing heat.

Some conventional after-treatment systems that employ catalyst beds to remove NOx and other emissions, do so by passing the engine exhaust through a bed, and when the bed requires regeneration the engine operating point is changed and the flow through the LNT is bypassed to some degree. The problem with such conventional systems and methods is that there still exists a significant amount of oxygen in the LNT. This oxygen must be removed to allow proper regeneration of the LNT. The present system uses a flow diverter to direct the exhaust gas flow away from the bed about to be regenerated and to a second bed that is then in trapping mode.

Alternative Designs and Modes of Operation

Fuels such as natural gas, CH₄, gasoline, methanol, propane, butane or other hydrocarbons could be used rather an diesel fuel.

The fuel used in the SGG could be the same as the primary fuel for the engine, or it could be a different fuel.

If the fuel supplied to the syngas generator is the same as the primary fuel for the engine, the same tank can supply both the engine and the syngas generator, or separate tanks can be used—whichever is more desirable for packaging and vehicle integration reasons.

The syngas generator can be a catalytic reactor.

An electrical heater could be used to assist in vaporizing diesel fuel during start-up of the SGG, especially cold start-up.

The pressure difference between the engine exhaust stream and the syngas gas stream could be deliberately reduced. Because the engine exhaust pressure is typically higher than the pressure of the syngas from the SGG, in some cases there can be leakage of engine exhaust gas into the exhaust after-treatment devices when they are being regenerated with syngas. For example, engine exhaust may leak across the upstream flow diverter to the syngas side in FIG. 5 a and 5 b. This is a waste of syngas. One way to address this problem is to throttle back the flow of syngas into the engine air intake line to increase the pressure of the syngas stream, and thus reduce such leakage across the flow diverter that is upstream of the LNTs.

Various fluid transfer devices could be used to control the mass flow of diesel fuel to the SGG instead of the diesel metering pump described above. These include:

-   -   (a) “Siphoning” the diesel fuel from the supply tank using the         ejector type effect created by using an ‘air assist’ spray         nozzle in the SGG.     -   (b) Using a centrifugal pump to create a substantially constant         pressure of diesel fuel, at a pressure that is matched to the         equipment, to admit the diesel fuel into the mixing portion of         the SGG. A proportional flow control valve could then be used to         control the mass flow of diesel fuel into the SGG.     -   (c) Tapping into a point in the fuel common rail. This         relatively high pressure point could then be attached to a         proportional valve that would receive a control signal from the         engine control module.

Also the diesel fuel could be pre-heated prior to mixing in the SGG. Heat can be drawn from the product syngas, from the engine exhaust, the engine coolant stream or another hot stream in the system or a combination of them using an appropriate heat exchanger. This could simplify the design of the SGG.

Potential alternatives or enhancements to the illustrated LNT configuration include:

-   -   (a) Placing two or more LNTs in series for trapping and then,         during regeneration, directing the engine exhaust stream to         bypass the regenerating bed(s).     -   (b) A small amount of syngas could be introduced into the LNT         while in trapping mode to maintain the LNT temperature at a         desired level.     -   (c) A separate and independent combustor could be employed to         create heat to keep the LNT beds at a desired temperature, which         could be controlled in turn by controlling amount of diesel fuel         directed to the combustor.     -   (d) Electrical heaters could be used to quickly heat the LNT to         the temperature at which NOx trapping and regeneration are best         carried out.     -   (e) The same electrical heaters could be used to keep the beds         at a desired trapping and regeneration temperature during all         modes of operation.     -   (f) The LNTs could be incorporated into a heat exchanger to         allow control of bed temperature to the desired temperature for         trapping and regeneration.     -   (g) Syngas could be used to keep the LNTs at the desired         temperature.     -   (h) The LNT portion could be combined or replaced with a         selective catalytic reduction (SCR) system.     -   (i) The SCR system could be either UREA- or HC-based. Either         could serve as the gross clean-up device and the other as the         fine clean-up device. The HC-SCR would preferably perform the         gross clean-up continuously and then the LNTs would be used to         perform the fine clean-up.

There may be some advantages to incorporating an SCR system in combination with one or more LNTs as mentioned above. Small quantities of ammonia (NH₃) can be a by-product formed during regeneration of LNTs. In SCR systems ammonia is used to chemically reduce NOx to nitrogen gas (N₂) and water, so it may be possible to use the ammonia by-product formed during regeneration of the LNTs as the reacting agent for the SCR.

A potential alternative to the techniques discussed above for controlling cycle timing is:

-   -   (a) Employing a closed loop having a NOx sensor, temperature         sensor, O₂ sensor, HC sensor or other constituent sensor, so         switching between regeneration and trapping modes is done based         on the sensing of actual values, instead of using a fixed cycle         time or algorithm for determining when to switch modes.

Potential alternatives or enhancements to the illustrated LNT structure include:

-   -   (a) A cylindrical bed or valve system where the LNT absorbent         bed, or gas distribution system is divided and sealed in a         radial pattern. Engine exhaust is allowed to flow through a         portion of the bed, allowing NOx from the exhaust to be trapped,         while syngas is allowed to flow through the remaining portions,         regenerating those portions of the bed. The bed or the gas         distribution system is rotated to switch the portions of the bed         from trapping mode to regeneration mode. This reduces the         overall size and complexity of the LNT bed and gas distribution         configuration.     -   (b) Use of sintered metal in the LNT as the substrate and         depositing catalyst on that substrate, thereby resulting in         lower pressure drops and greater flow rate and permitting the         use of smaller bed size.         Potential End-Uses for the Present After-Treatment System

The present systems can be applied to on-road vehicles, off-road vehicles, stationary power generation, and marine applications.

The applications above could be diesel-fueled or fueled by gasoline, natural gas, propane, butane or similar fuels.

A similar design and method of operation of the SGG and associated components can be used to introduce syngas into the air intake of lean burn engines, for example lean burn gasoline engines. This will extend the lean burn limit of the in-cylinder combustion and allow higher air/fuel ratios leading to reduced emissions and improved fuel economy.

The addition of syngas to the air intake stream changes the combustion properties of the combustion charge. This may allow further modifications to the engine, for example air/fuel ratios, fuel injection properties (timing, pressure, spray pattern), compression properties (compression ratios, compression chamber profile). Thus, integration of the SGG with the engine can allow modification of the combustion charge and its properties to allow lower emissions and increased fuel economy.

The SGG could also be integrated with a fuel cell power generator to produce auxiliary power for a vehicle. This allows for increased electrification of the vehicle and thus to lower costs and increased efficiency especially for reduction of idling time. The fuel cell power generation system could be a hybrid system that allows the fuel cell to stay on continuously and charge an energy storage device. The fuel cell could be, for example, a solid oxide fuel cell or a proton exchange membrane fuel cell.

The SGG could be used to create heat to warm the engine, engine oil, thermal-electric generating device or operator compartment of a vehicle when the engine is turned off.

The syngas produced in the system could be used for homogeneous charge compression ignition (HCCI) where addition of syngas to the air intake stream may enhance the combustion process.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings. 

1. A method of operating an engine system comprising an exhaust after-treatment system and a syngas generator, the method comprising: (a) directing a fuel stream from a fuel supply to said engine, and directing an air stream to said engine via an air intake line, and operating said engine to produce an engine exhaust stream; (b) operating said syngas generator to produce a syngas stream; (c) at least periodically directing at least a portion of said engine exhaust stream to at least one exhaust after-treatment device in said exhaust after-treatment system, for reducing regulated emissions from said engine system; (d) at least periodically directing at least a portion of said syngas stream to said at least one exhaust after-treatment device for heating or regenerating said device, thereby producing a depleted syngas stream; (e) directing a surplus syngas stream to said engine via said air intake line.
 2. The method of claim 1 wherein said surplus syngas stream comprises said depleted syngas stream.
 3. The method of claim 1 wherein said surplus syngas stream comprises the portion of said syngas stream that is not directed to said at least one exhaust after-treatment device.
 4. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a venturi or ejector in said air intake line.
 5. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a particulate filter.
 6. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a sulfur trapping bed.
 7. The method of claim 1 wherein said surplus syngas stream is introduced into said air intake line upstream of an engine intake air compressor.
 8. The method of claim 1 wherein at least a portion of said engine exhaust stream is recirculated to said engine via an exhaust gas recirculation line.
 9. The method of claim 1 wherein the quantity of surplus syngas directed to said engine via said air intake line is adjusted in accordance with an operating parameter indicative of the engine power output demand.
 10. The method of claim 9 wherein the operating parameter is the accelerator position, or air intake mass flow or the engine speed.
 11. The method of claim 9 wherein the rate of production of syngas is adjusted in accordance with an operating parameter indicative of at least one of: the level of regulated emissions in said engine exhaust stream, oxygen content in the engine exhaust stream, air intake mass flow, engine speed and engine power output demand.
 12. The method of claim 11 wherein the rate of production of syngas, and the quantity of surplus syngas directed to said engine via said air intake line, are both increased in response to an increase in at least one of the level of regulated emissions in said engine exhaust stream and the engine power output demand.
 13. The method of claim 1 wherein fuel from said fuel supply and at least a portion of said engine exhaust stream are directed to said syngas generator and reacted therein to produce said syngas.
 14. The method of claim 13 wherein the flow rate of said engine exhaust stream to said syngas generator is passively controlled.
 15. The method of claim 1 wherein said syngas generator is operated whenever said engine is operated.
 16. The method of claim 1 wherein said regulated emissions comprise NOx, particulate matter and hydrocarbons.
 17. The method of claim 1 wherein said exhaust after-treatment system comprises at least one lean NOx trap.
 18. The method of claim 1 wherein said exhaust after-treatment system comprises a pair of lean NOx traps.
 19. The method of claim 18 wherein an engine exhaust gas flow diverter, located upstream of said pair of lean NOx traps, alternates between directing at least a portion of said engine exhaust stream to a first and then a second one of said pair of traps at the same time as a syngas gas flow diverter, located upstream of said pair of lean NOx traps, alternates between directing at least a portion of said syngas stream to the second and first of said pair of traps respectively, for regenerating said traps.
 20. The method of claim 19 wherein at least one downstream flow diverter located downstream of said pair of lean NOx traps alternately directs said depleted syngas stream from whichever one of said pair of traps is being regenerated to said engine via said air intake line.
 21. The method of claim 18 wherein a combined upstream flow diverter located upstream of said pair of lean NOx traps directs at least a portion of said engine exhaust stream to a first one of said pair of traps and at the same time directs at least a portion of said syngas stream to the second of said pair of traps for regenerating said second trap, alternately with directing at least a portion of said engine exhaust stream to the second one of said pair of traps at the same time as directing at least a portion of said syngas stream to the first of said pair of traps for regenerating said first trap.
 22. The method of claim 20 wherein at least one downstream flow diverter located downstream of said pair of lean NOx traps alternately directs said depleted syngas stream from whichever one of said pair of traps is being regenerated to said engine via said air intake line.
 23. The method of claim 18 wherein each of said pair of lean NOx traps is switched between operating in a regenerating mode and in a trapping mode, so that when one is in a regenerating mode the other is in a trapping mode.
 24. The method of claim 23 wherein said switching of said traps between a regenerating mode and a trapping mode is performed based on a fixed cycle time or algorithm.
 25. The method of claim 22 wherein said switching of said traps between a regenerating mode and a trapping mode is performed and adjusted based on a monitored operating parameter.
 26. The method of claim 25 wherein said operating parameter is an operating parameter determined by at least one of a NOx sensor, a temperature sensor, and oxygen sensor, a hydrocarbon sensor.
 27. The method of claim 23 wherein the duration of each said trapping mode less than about 20 seconds.
 28. The method of claim 27 wherein the duration of each said regeneration mode is about the same as the duration of each said trapping mode.
 29. The method of claim 28 wherein the duration of each said regeneration mode and of each said trapping mode is about 10 seconds.
 30. The method of claim 1 wherein the syngas generator is a non-catalytic reactor.
 31. A combustion engine and after-treatment system comprising: (a) a fuel tank and fuel supply subsystem for directing fuel to said engine; (b) an air supply subsystem for directing air to said engine stream via an air intake line; (c) an engine exhaust stream line connected to receive an exhaust stream from said engine; (d) at least one exhaust after-treatment device actuatably fluidly connected to said engine exhaust stream line; (e) a syngas generator comprising a syngas output line actuatably fluidly connected to said at least one exhaust after-treatment device; wherein said air intake line is fluidly connected receive surplus syngas from at least one of said exhaust after-treatment device and said syngas output line.
 32. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive surplus syngas from said exhaust after-treatment device and from said syngas output line.
 33. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a venturi or ejector located in said air intake line.
 34. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a particulate filter.
 35. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a sulfur trapping bed.
 36. The combustion engine and after-treatment system of claim 31 wherein said air supply subsystem comprises a compressor and wherein said air intake line is fluidly connected to receive said surplus syngas upstream of said compressor.
 37. The combustion engine and after-treatment system of claim 31 further comprising a controller for adjusting the quantity of surplus syngas directed to said engine via said air intake line in accordance with an operating parameter indicative of the engine power output demand.
 38. The combustion engine and after-treatment system of claim 31 wherein said controller is also for adjusting the rate of production of syngas in accordance with an operating parameter indicative of at least one of: the level of regulated emissions in said engine exhaust stream, oxygen content in the engine exhaust stream, air intake mass flow, engine speed and engine power output.
 39. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is fluidly connected to said engine exhaust stream line for receiving at least a portion of said engine exhaust stream.
 40. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is fluidly connected to said fuel tank and fuel supply subsystem for receiving said fuel.
 41. The combustion engine and after-treatment system of claim 31 wherein said exhaust after-treatment system comprises at least one lean NOx trap.
 42. The combustion engine and after-treatment system of claim 31 wherein said exhaust after-treatment system comprises a pair of lean NOx traps.
 43. The combustion engine and after-treatment system of claim 42 wherein each one of said pair of lean NOx traps is alternatingly fluidly connected to said engine exhaust stream line and to said a syngas generator via a flow diverter located upstream of said pair of traps.
 44. The combustion engine and after-treatment system of claim 42 wherein said air intake line is fluidly connected receive depleted syngas alternately from each one of said pair of lean NOx traps via a flow diverter located downstream of said pair of traps.
 45. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is a non-catalytic reactor.
 46. The combustion engine and after-treatment system claim 31 further comprising an exhaust gas recirculation line fluidly connecting said engine exhaust stream line to said air intake line.
 47. A method of mitigating a combustion engine exhaust stream comprising nitrogen oxides, the method comprising: (a) operating a reducing agent generator to produce a reducing agent stream; (b) in a trapping mode, introducing at least a portion of said engine exhaust stream into at least one catalytic lean NOx trap; (e) in a regeneration mode, introducing at least a portion of said reducing agent stream said at least one lean NOx trap, wherein the duration of each said trapping mode is less than about 20 seconds.
 48. The method of claim 47 wherein the duration of each said regeneration mode is about the same as the duration of each said trapping mode.
 49. The method of claim 48 wherein the duration of each said regeneration mode and of each said trapping mode is about 10 seconds.
 50. The method of claim 47 wherein said reducing agent generator is a syngas generator and said reducing agent is syngas.
 51. The method of claim 50 wherein a fuel stream and at least a portion of said engine exhaust stream are directed to said syngas generator to produce said syngas stream.
 52. The method of claim 47 wherein in said trapping mode said engine exhaust stream flows through said catalytic lean NOx trap in a direction substantially opposite to the direction that said reducing agent stream flows through said catalytic lean NOx trap in said regeneration mode.
 53. The method of claim 47 wherein said after-treatment module comprises a first lean NOx trap and a second lean NOx trap, said method further comprising alternatingly directing said engine exhaust stream and said reducing agent stream via said upstream flow diverter such that when said first lean NOx trap is in said trapping mode, said second lean NOx trap is in said regeneration mode, and when said first lean NOx trap is in said regeneration mode, said second lean NOx trap is in said trapping mode.
 54. A method of operating an engine system with improved fuel economy, the engine system comprising an exhaust after-treatment system and a syngas generator, the method comprising: (a) injecting a fuel stream from a fuel supply to said engine, and directing an air stream to said engine via an air intake line, and operating said engine to produce an engine exhaust stream, wherein the timing of the fuel injection is selected for improved fuel economy but so that the level of regulated emissions in said engine exhaust stream, upstream of said exhaust after-treatment system, at least periodically exceeds regulation levels; (b) operating said syngas generator to produce a syngas stream; (c) at least periodically directing at least a portion of said engine exhaust stream to at least one exhaust after-treatment device in said exhaust after-treatment system, for reducing regulated emissions from said engine system below said regulated levels; (d) at least periodically directing at least a portion of said syngas stream to said at least one exhaust after-treatment device for heating or regenerating said device;
 55. The method of claim 54 wherein engine exhaust gas is not recirculated to the engine. 